1. Field of the Invention
The present invention relates to machine safety and in particular to safety sensing systems for use with pressing type machines. In the present context "pressing type machines" is intended to include all industrial machines which have at least one reciprocally movable operating head, tool, ram or beam.
2. Description of the Prior Art
The potential for accidental injury during the operation of many types of industrial machines has resulted in the production of numerous devices to guard such machines. In this connection most machines are subject to strict government regulations which require that a guarding system meeting certain specified requirements be fitted to the machine before it can be operated. Numerous types of industrial machines cannot be guarded in the required manner by mechanical devices without resulting in a loss of productivity and/or a restriction on the operation of the machine.
Systems employing optical detection devices have been developed to overcome these difficulties and such systems generally comprise a light beam "barrier" between the operator and the machine. The barrier is typically formed from a number of parallel and co-planar light beams. When the light beam "barrier" is broken, the safety system operates to immobilise or slow the machine in some manner. These systems still suffer from limitations similar to mechanical guard systems particularly when used with machines such as pressing type machines which may require the operator to place a job under the pressing tool.
The major difficulty is that the beam used in the guard system cannot be located so close to the machine that it is broken by the material being pressed during the pressing operation and at the same time the beam cannot be located so far away from the machine that the danger area is accessible to the operator, for example, without breaking the beam.